JPH0244037B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF THE INVENTION The present invention relates to ceramic technology and the production of sintered bodies of non-metallic powders, and more particularly:
The present invention relates to novel nuclear fuel powder and binder mixtures and green bodies made from such mixtures having unique physical properties, as well as novel methods of manufacturing such mixtures and green bodies thereof. BACKGROUND OF THE INVENTION Although a variety of materials have been used as nuclear fuel for nuclear reactors, including ceramic compounds of uranium, plutonium, and thorium, particularly preferred compounds are uranium oxide, plutonium oxide, thorium oxide, and mixtures thereof. It is. Among them,
A particularly suitable nuclear fuel for use in nuclear reactors is uranium dioxide. Uranium dioxide is commercially produced as a fine, highly porous powder, but it cannot be used directly as a nuclear fuel. Since this powder is not in a free-flowing state and contains agglomerates and agglomerates, it is difficult to pack it into the fuel tube at the desired density. Furthermore, due to the composition of commercially available uranium dioxide powder, it cannot be used directly as a nuclear fuel. Uranium dioxide forms an exception to the law of definite proportions. Thus, although uranium dioxide does form a single stable phase, its composition can vary from _1.7 UO to _2.27 UO. Since thermal conductivity decreases as the O/U ratio increases, uranium dioxide with as low an O/U ratio as possible is preferred. However, since uranium dioxide powder easily oxidizes in air and easily absorbs moisture, the O/U ratio of such powder significantly exceeds the value suitable for nuclear fuel use. Several methods have been used to adapt uranium dioxide for nuclear fuel use. at present,
The most common method is to press the powder into cylindrical compacts of predetermined dimensions. However, the various organic or plastic binders commonly used to facilitate the production of compacts of powdered material prior to sintering are not applicable to nuclear fuels. This is because they tend to contaminate the interior of the sintered body with impurities such as hydrides. Typically, such binders are converted to gas during the sintering process and are
Such gases must be removed, requiring special equipment or operations. If you disassemble it again,
Conventional binders typically deposit organic materials within the equipment used for sintering the product, making the equipment cumbersome to maintain. Additionally, conventional carbon-containing binders also leave carbon residue in the nuclear fuel because calcination is performed in a reducing atmosphere that results in thermal decomposition of the polymeric material. These deficiencies of the prior art have been significantly improved by the invention of Gallivan, US Pat. No. 4,061,700, issued December 6, 1977, assigned to the same assignee as the present invention. According to this invention,
By using a binder consisting of uranyl ammonium carbonate, uranyl ammonium bicarbonate, or uranyl ammonium carbamate, the compacted or green body remains cohesive throughout handling and processing operations up to the final sintering step. It will be done. More specifically, in producing compacted bodies or green bodies in accordance with the invention, UO ₂ granules containing about 5% uranyl ammonium carbonate, for example, by contacting with ammonium bicarbonate, A homogeneous mixture is produced. The density of compacts produced from such mixtures corresponds to approximately 30-70% of the theoretical value, depending on the applied pressure used, but sometimes reaches 90%. When produced by conventional batch pressing operations, such as using hydrometallurgical presses, such compacts have sufficient strength to give relatively high yields of acceptable product. However, in the case of continuous operation using a rotary press, it cannot be said that the compressed body can sufficiently withstand the accompanying pressurizing force conditions. SUMMARY OF THE INVENTION The present inventors have now discovered that compressed nuclear fuel bodies having relatively high tensile strength can be consistently produced. Moreover, such a result
It has been found that a moderate compression force of 20,000 pounds per square inch (1406 kg/cm ² ) can be obtained. Furthermore, such compressed bodies have very high tensile strength or a unique combination of high tensile strength and substantial plasticity, so that they can be produced with high yields even in continuous operations involving the use of rotary presses. found. Moreover, these advantages are achieved without significant process complexity, increased product cost, or significant tradeoffs. In summary, the present invention provides a method for reacting nuclear fuel containing uranyl ammonium carbonate, uranyl ammonium bicarbonate, or uranyl ammonium carbamate with an amine under specific conditions, thereby making it more suitable than uranyl ammonium carbonate as a binder for particulate nuclear fuel material. The idea is to produce advantageous water-soluble uranyl compounds. Preferably, the amine described above is a polyfunctional primary amine and the reaction of the present invention involves contacting such amine with a particulate mixture of nuclear fuel material prepared as described in the aforementioned patent specification. This will be implemented by Considering that ammonia is liberated in each case in an amount approximately proportional to the amount of amine added, it is believed that the compound resulting from the above reaction is the amine corresponding to the original uranyl ammonium compound. In any case, the end result is a binder that is more effective for continuous production, for example by rotary press operations. Conditions favorable for such a reaction have been found to be standard conditions consisting of room temperature, normal humidity and atmospheric pressure. However, some heating may sometimes be preferable, particularly when the amine is a solid at room temperature or when the rate of ammonia release reaction is too slow. Furthermore, excess amine beyond that required to completely replace ammonia and produce a more effective binder can be detrimental to the tensile strength and plasticity of the resulting green compact of nuclear fuel material. It was also found that this could be the case. For example, in the example below, a compact obtained by adding a slight excess of ethylenediamine to a uranium dioxide powder containing uranyl ammonium carbonate is a compact of the same powder without amine addition. It showed only the same plasticity and tensile strength as the body. Generally speaking about the method aspects of the present invention, the method of the present invention provides a particulate form of a water-soluble uranyl compound that has substantially increased effectiveness as a binder by reacting the uranyl ammonium compound with an amine. The main step is to form the mixture in situ. This step precedes the step of press-molding the particulate mixture to form a compressed body for sintering having the size and shape of a nuclear fuel pellet. This process also involves contacting a liquid, solid, or gaseous amine with a particulate or powder mixture, such as a uniform distribution of uranyl ammonium carbonate or its equivalent on the surface of individual particles of nuclear fuel material. It consists of As mentioned above, the working conditions in this case are favorable for the ammonia substitution reaction. As a result, it is envisioned that at least 35% of the ammonia in the uranyl ammonium compound is liberated, and the uranyl ammonium compound itself is replaced by the amine. In accordance with the best practice of the invention, the amount of amine added is such that at the end of ammonia liberation, substantially no unreacted amine remains in the powder mixture. Similarly, speaking generally about the material composition aspect of the present invention, the particulate nuclear fuel material of the present invention is a nuclear fuel material containing a small amount of a water-soluble uranyl compound different from uranyl ammonium carbonate, uranyl ammonium bicarbonate, or uranyl ammonium carbamate. It consists of a powder mixture of Such a minor component serves as an excellent binder for the compact of the powder mixture and consists, for example, of the reaction product of uranyl ammonium carbonate with an amine and is present in a proportion of about 0.5 to 7%. It is also
As mentioned above, it is preferably derived from a polyfunctional primary amine or a mixture of two or more thereof. Next, I will briefly describe the product aspect of the present invention.
The products of the invention are made from particulate nuclear fuel material (e.g. UO 2 ) bound by small amounts of water-soluble uranyl compounds that are better binders than uranyl ammonium carbonate, uranyl ammonium bicarbonate or _uranyl ammonium carbamate. It is a pellet-shaped unsintered compressed body consisting of As mentioned above, the compressed body preferably contains the water-soluble uranyl compound described above in a proportion of about 0.5 to 7%, and the water-soluble uranyl compound is preferably derived from a polyfunctional primary amine. . In accordance with the best practice of the present invention, as with the starting particulate nuclear fuel material, such compacted bodies will be substantially free of residual unreacted amine. The invention will now be described in more detail with reference to the accompanying drawings. DETAILED DESCRIPTION OF THE INVENTION In practicing the present invention, a UO ₂ powder mixture containing uranyl ammonium carbonate is prepared as shown in the process diagram of FIG. In that case, uranyl ammonium carbonate is prepared in situ by contacting the powder with ammonia, carbon dioxide and water vapor under conditions favorable for the reaction to obtain the desired product uniformly distributed in the powder. It is preferable to generate The mixture thus obtained is referred to herein as "treated powder." Alternatively, the required content of binder can be obtained by adding finely divided ammonium bicarbonate and thoroughly mixing both powders, following the route indicated by the dotted line in the figure. After a period of up to 10 days, UO ₂
A uranyl ammonium carbonate binder is obtained by reaction of the powder with added ammonium bicarbonate. That is, under standard temperature, pressure and humidity conditions (26°C, atmospheric pressure, 74% relative humidity) ammonium bicarbonate decomposes into ammonia, carbon dioxide and water vapor, which then react with _UO2.
This produces uranyl ammonium carbonate on the surface of the UO ₂ particles. In a step in the process, the mixture thus obtained is contacted with a suitable amine under conditions favorable for the reaction to replace the ammonia in the binder with the amine. This step is a new and major step in the process and is essential to consistently achieve the novel results and advantages described above. For such purposes it is preferred to use 1,3-diaminopropane. It can be added as a liquid or gas or even as a solid, but according to a preferred embodiment it is used as a liquid. When added as a solid, the amine may be frozen and ground into a fine powder, and then the two powders may be thoroughly mixed. As the temperature of the amine increases, the displacement reaction begins, as evidenced by the evolution of ammonia from the mixture. Alternatively, the amine can be vaporized and diffused into the powder, thereby reacting with the ammonium compound to liberate ammonia. Although polyfunctional primary amines are used alone according to the preferred embodiment of the invention, it is understood that other amines can be used and mixtures of amines are also suitable for the purposes of the invention. I want to be Similarly, although 1,3-diaminopropane is preferred, other amines may be preferred due to commercial availability or other practical reasons. Currently particularly preferred substitute amines include ethylenediamine, monomethylamine, 1,6-diaminohexane and 1,7-diaminoheptane. For most amines, the practitioner is free to choose the form in which they are used. However, in the case of monomethylamine, it is a gas at room temperature, so
Using an alternative method is not easy. Similarly, 1,
6-diaminohexane and 1,7-diaminoheptane are solid at room temperature, and therefore cannot be easily used as a gas. As shown by curves B and C in FIG. 2, 1,3-diaminopropane provides significantly better pellet properties. It also reacts rapidly under standard conditions to result in the displacement of ammonia, thereby treating the treated powder or UO ₂ powder obtained from the selectable preliminary steps shown respectively by the solid and dotted lines in the process diagram of Figure 1. -Produces superior binder in an amount approximately proportional to the initial uranyl ammonium compound content of the binder mixture. The data shown by curves A, B and C represent powder mixtures in each case at 20 kpsi (1406 Kg/cm ³ ).
The tensile strength of each compressed body in the form of a standard nuclear fuel pellet was measured by conventional methods. More specifically, Curve B is a test of pellets made by treating the powder of Curve A according to the present invention to replace about 40-45% of the ammonia in the binder with 1,3-diaminopropane. It represents the data obtained at the time. Curve C also represents data obtained in tensile testing of pellets made from the powder of curve A by replacing 70-80% of the ammonia with the same amine. Curve A,
Comparing the results represented by B and C, it can be seen that replacing 75% ammonia according to the invention increases the tensile strength by a factor of 3 compared to the unsubstituted product of curve A; Replacement of ammonia increases the same properties more than twice. Furthermore,
The relative effectiveness of the amine reaction depends on the gas (CO ₂ ,
The amount of ammonium bicarbonate that must be added to produce the same amount of uranyl ammonium carbonate as that produced by the NH ₃ , H ₂ O) treatment is slightly greater in the lower range of equivalent ammonium bicarbonate content. ing. processed in this way
Pellets made from UO ₂ powder were tested up to 37 days after amine addition, and no changes in properties were observed, but no tests were conducted after that point. Please note that at the beginning of this process
Regarding the composition of the UO ₂ powder and the method for its preparation, it is advantageous to follow the detailed description found in the Gallivan patent specifications, such as those mentioned above. The portions of this patent that address the above issues are incorporated herein by reference in their entirety. Furthermore, when referring to nuclear fuel materials, it should be understood that the terms and expressions used herein are as defined generally and in detail in the Gallivan patents, referenced above. EXAMPLES The following examples are provided to explain the novel features and advantages of the present invention in more detail, but the scope of the present invention is not limited thereby. Example 1 Ammonia, carbon dioxide, water vapor and oxygen in 500 g of UO ₂ powder were flowed over a period of 20 hours.
Ambient conditions during such operations were maintained at a temperature of 26°C, humidity of 74%, and atmospheric pressure. Also, the gas flow rate is almost constant, and the values for ammonia, carbon dioxide, and oxygen are 0.12, 0.09, and 0.09, respectively.
It was 4.6/min. At the end of the above work, it was found that the weight of the powder had increased by 4.8% due to the formation of uranyl ammonium carbonate. The same amount of uranyl ammonium carbonate can be produced by adding 6.0% ammonium bicarbonate and aging for up to 10 days. Therefore, the equivalent ammonium bicarbonate content in this example is 6.0%. After storing the powder thus treated in a closed container for 2.5 months, the tensile strength of pellets made from the powder was estimated to be 200 psi (14 Kg/cm ³ ). This value was not actually measured in this example, but was obtained by actually measuring the tensile strength of pellets produced from the powder after similar treatment and ripening. Ethylenediamine vapor was then passed through the powder. That is, oxygen was passed through pure ethylenediamine at 22° C. at 1 part per minute, and then the oxygen was passed through 500 g of treated powder over a period of 3.5 hours. Thereafter, unreacted ethylenediamine was removed from the treated powder by flowing pure oxygen at 1 per minute for 5 minutes. It was found that after such (operation) the weight of the treated powder increased by 0.85%. The powder thus obtained was heated at 20 kpsi (1406
The tensile strength of the pellets produced by pressing at 333 psi (23.4 Kg/cm ³ ) was found to be 333 psi (23.4 Kg/cm ³ ). Example 2 Under conditions as described in Example 1, 1
Kg of _UO2 powder was treated with ammonia, carbon dioxide, water vapor and oxygen for 18 hours. As a result, the weight of the treated powder increased by 3.6% and the pellets produced by pressing the treated powder at 20 kpsi (1406 Kg/cm ³ ) increased to 152 psi (10.7
It had a tensile strength of Kg/cm ³ ). Ethylenediamine vapor was passed through 200 g of the above treated powder using the same procedure as in Example 1 without aging. As a result, a weight increase of 1.23% was observed. Pellets of standard size and shape made by pressing the powder thus obtained at 20 kpsi had a tensile strength of about 366 psi (25.7 Kg/cm ³ ). The original UO ₂ used in the two examples above
The powder (ie, untreated UO ₂ powder) was pressed at 20 kpsi to yield pellets with a tensile strength of approximately 35 psi (2.5 Kg/cm ³ ). Therefore, as a result of the simultaneous treatment with ammonia, carbon dioxide, water vapor and oxygen, as well as the treatment with ethylenediamine, the tensile strength of the resulting green pellets was increased approximately 10 times. Example 3 As an experiment to test the usefulness of liquid amines in the process of the invention, 1/2 cm ³ of liquid ethylenediamine was added to 50 g of UO ₂ powder prepared as described in Example 1. Each was added four times. When the mixture was vigorously stirred, ammonia gas evolution was observed, but this stopped within a few minutes. 0.86 mol of ammonia was liberated per 1 mol of ethylenediamine added. The resulting powder was pressure molded and measured in a conventional manner to yield 300 psi (21.1 psi).
A tensile strength exceeding Kg/cm ³ ) was observed. Example 4 To demonstrate that 1,3-diaminopropane is particularly useful in the process of the invention, liquid 1,3-diaminopropane is added to the UO ₂ powder prepared as described in Example 1. An experiment was conducted in which . That is, as described in Example 2, 1,3-diaminopropane was added to 50 g of UO ₂ powder in four 1/2 cm ³ portions. After 5 minutes, the reaction was complete as evidenced by the end of ammonia evolution. A test was conducted on a pellet-shaped compressed body produced by pressure-molding the mixture thus obtained at 20 kpsi (1406 Kg/cm ³ ). The results of these tests are shown in line 5 of Table B below. Example 5 A powder prepared as described in Example 1 was tested for changes in properties over time over a period of three weeks. The results thus obtained are shown in Table A below.

[Table] * ^f3 is a measure of plasticity and is the distance (in microns) that the test element of the Instron testing machine moves after the pellet breaks and before the pressing force is reduced to less than 90% of the maximum value. represent Example 6 To test the effectiveness of other amines and various proportions of 1,3-diaminopropane in the process of the invention, UO ₂ powder prepared as described in Example 1 was used. I conducted a test. However, the equivalent ammonium bicarbonate content was varied. The results of such tests are shown in Table B below, and these data were obtained by carrying out tensile tests and plasticity tests, also as described above, on compressed bodies produced as described above from the individually treated powders. This is what was obtained. As expected B
As is clear from the table, there is a linear but non-stoichiometric relationship between the amount of 1,3-diaminopropane added and the amount of ammonia displaced by the reaction of the invention. Note that similar linearity is expected for all of the amines tested.

【table】

TABLE The amines tested in this experiment were used in forms particularly suitable for the purposes of the invention, ie liquid, gaseous or solid. Specifically, monomethylamine was used in gaseous form and was passed into the treated powder commonly used in each of the tests in Table B. 1,7-diaminoheptane and 1,6-diaminohexane were used in solid form and were reduced to a powder state and then mixed with the treated powder described above. Other amines were used in liquid form and were mixed with the treated powder as described above. As can be seen from the results shown in the Examples above, especially from Example 6, it is clear that polyfunctional primary amines are particularly advantageous in the practice of the present invention. Furthermore, it is understood that 1,3-diaminopropane is probably the most suitable for use in the present invention because it provides rapid reaction and provides significantly better pellet properties as shown in FIG. It will be. However, in terms of commercial availability, 1,6-
In some cases, diaminohexane may be more suitable. In this case, some heating (up to about 60°C) may be necessary to complete the reaction. As can be seen from the general and detailed descriptions above and the experimental results detailed in the examples above, polyfunctional primary amines are generally used in accordance with preferred embodiments. However, it should be understood that the use of monofunctional amines, and also any amines that consistently provide the novel results and advantages of the present invention, is contemplated. Furthermore, as understood from the results shown in Table B, 1,3-diaminopropane,
Particular preference is given to using amines selected from the group consisting of 1,6-diaminohexane, 1,7-diaminoheptane, 3,3-diaminodipropylamine, ethylenediamine and mixtures thereof. Furthermore, depending on the amine or amine mixture used and the equipment used, such amines can be used in liquid, gaseous or solid form in accordance with the above description and in each case achieve the objects of the invention. It is possible. Example 7 To test the effect of an excess of amine over the amount required to completely remove ammonia in a treated powder of uranium dioxide, 0.0081 mol of (NH ₄ ) ₄ UO ₂ (CO ₃ ) ₃ was 50g of processed powder containing
0.0401 mole of ethylene diamine was added. As a result, 0.0326 mol of ammonia was generated. Assuming that 0.86 mole of ammonia is liberated by the addition of 1 mole of ethylenediamine as mentioned above, 0.0401 mole of ethylenediamine is in excess of 6% compared to the amount required to completely remove ammonia. Ta. Pellets prepared as described above from the powder thus obtained were tested and found to have a tensile strength of 96 psi and f ₃
The value was zero. As can be seen from the results of Example 7, as a practical matter, the amount of amine added to the treated powder when carrying out the process of the invention should not exceed 80-90% of the amount required to completely remove ammonia. should be. This is because, although the properties of the compressed body can be improved until the ammonia removal rate reaches 100%, if amine is added beyond this point, a significant decrease in the same properties may be observed. As used herein, "nuclear fuel material" refers to nuclear fuel material as defined in the aforementioned Gallivan patent. The method of the present invention is equally applicable to each of these nuclear fuel materials alone or to a mixture thereof. However, such a nuclear fuel material contains, for example, uranyl ammonium carbonate, and according to the present invention, a substitution reaction with an amine occurs, and the reaction product is a water-soluble uranyl compound, and this water-soluble uranyl compound is formed into particulates. Acts as a binder for nuclear fuel materials and exhibits better effectiveness than uranyl ammonium carbonate. In addition, when percentages and ratios are described in this specification, they are all based on weight.

[Brief explanation of drawings]

Figure 1 shows the treatment of UO ₂ powder with gas or
₂ is a process diagram illustrating the method of the present invention including optional preliminary steps for obtaining uranyl ammonium carbonate mixed with a high percentage of UO _{2 powder by mixing UO 2} powder with ammonium bicarbonate; FIG. ,
Figure 2 also shows the tensile strength of a compacted UO ₂ powder compacted at 20kpsi as defined in the text.
A graph plotted against the equivalent ammonium bicarbonate content of UO ₂ powder, where the three curves represent approximately 45% of the ammonia in uranyl ammonium carbonate, a powder mixture containing an unsubstituted ammonium compound binder. A similar powder mixture with displacement by amine reaction and a similar powder mixture with up to about 75% ammonia displacement are shown.

Claims (1)

[Scope of Claims] 1. A method for producing an unsintered compressed body of nuclear fuel material, comprising the step of press-molding a granular mixture of nuclear fuel material and a uranyl ammonium compound to form an unsintered compressed body, comprising: Prior to the pressure forming step, the uranyl ammonium compound is reacted with an amine compound to eliminate ammonia, and a water-soluble uranyl compound is formed in the mixture as a binder for the mixture. A method characterized by comprising: 2. The method according to claim 1, wherein the uranyl ammonium compound is uranyl ammonium carbonate, uranyl ammonium bicarbonate, or uranyl ammonium carbamate. 3. The method of claim 1, wherein the amine compound is 1,3-diaminopropane, 1,6-diaminohexane, 1,7-diaminoheptane, monomethylamine, ethylenediamine or a mixture thereof. 4. Where the amine compound is 1,3-diaminopropane, the amine compound is added to the mixture as a liquid and is applied substantially uniformly throughout the mixture onto the surfaces of individual particles of the nuclear fuel material. The method of claim 1 as distributed. 5. Where the amine compound is 1,6-diaminohexane, the amine compound is added as a finely divided solid and mixed with the particulate nuclear fuel material, and the resulting mixture is heated to 60° C. by about 1/2 2. The method of claim 1, wherein heating is performed for 2 hours to promote the reaction of the amine compound and the formation of the water-soluble uranyl compound. 6. The method of claim 1, wherein the water-soluble uranyl compound is produced by contacting gaseous ethylenediamine with the particulate nuclear fuel material and reacting with the uranyl ammonium compound. 7. Claim 1, in which a uranyl ammonium compound is mixed into a nuclear fuel material to prepare a particulate mixture, and an amine compound is added to the mixture in a ratio less than the stoichiometric equivalent of the uranyl ammonium compound. The method described in section. 8. The method of claim 7, wherein said amine compound is added at a rate of about 80% of the amount necessary to completely eliminate ammonia from said uranyl ammonium compound. 9 Consists of nuclear fuel particulate material containing a small but effective amount of a water-soluble uranyl compound, which is the reaction product of an amine and uranyl ammonium carbonate, and which maintains the integrity of the pellet through processing operations up to the final sintered state. A compacted green product formed into pellets with sufficient tensile strength and plasticity to maintain 10. The green compressed product according to claim 9, which contains a residual uranyl ammonium compound. 11. The unsintered compact product according to claim 9, which does not substantially contain unreacted residual amine compounds.